In 2005 a pool of institutions formally initiated a process via the Brazilian Environmental Agency (IBAMA) to create a full protection conservation unit encompassing the Camurupim/Cardoso and Timonha/Ubatuba estuaries, state of Piauí, NE Brazil. Among the flagship species to generate support for the protection of those estuaries is the seahorse Hippocampus reidi, focus of the present study. The results of our one-year survey in that area revealed the occurrence of resident population of H. reidi, found in 19 distinct habitats and with one of the highest densities already reported for the species (0.04 ind/m2). This information highlights the crucial need to further support the protection of that area, which aside from housing H. reidi, a species listed as Data Deficient by the World Conservation Union (IUCN), is also an area of occurrence of the Leatherback Turtle (Dermochelys coriacea), species considered as Critically Endangered, and the American Manatee (Trichechus manatus manatus) a Vulnerable species, according to the IUCN Red List of Threatened Species 2008.